The present invention is related to the field of fiberoptic devices and networks, and more particularly, provides optical fiber packages which vary tension in an optical fiber, particularly for compensating for temperature induced wavelength variations in fiber Bragg gratings.
Modern fiberoptic communication systems often have the ability to simultaneously transfer light signals having differing wavelengths over a single optical fiber.
Fiber Bragg gratings are a particularly advantageous structure for differentiating and manipulating optical signals based on their wavelength. Fiber Bragg gratings are often formed by selectively exposing photosensitive fiber to light, thereby creating a permanent refractive-index grating along the core of the fiber. Sharp reflection resonances can be used as demultiplexers, laser diode wavelength stabilizers, external laser mirrors, dispersion compensators, and the like. Fiber Bragg gratings also have applications in communications and sensor areas, operating as resonators, filters, pressure sensing elements, etc. Therefore, fiber Bragg gratings are expected to be important components in many optical communication systems, particularly in the dense wavelength division multiplex systems now being developed.
Unfortunately, fiber Bragg gratings often have a significant temperature sensitivity. For example, the resonant wavelength of a fiber Bragg grating may vary as much as 0.01 nm per degree centigrade. This temperature sensitivity is significantly higher than the sensitivity of resonators and/or filters formed using thin-film coating techniques, which typically provide resonant frequencies which vary about 0.003 nm per degree centigrade. Their large temperature sensitivity mitigates the cost advantages and precise wavelength control otherwise provided by fiber Bragg gratings, thereby limiting their acceptability.
To overcome the disadvantageous sensitivity of fiber Bragg gratings to changes in temperature, a variety of temperature compensation packages have been proposed. Known compensation packages generally rely on fiber support structures having one or more materials which are affixed to the fiber so as to compensate for the thermal expansion of the fiber material. Unfortunately, to overcome the disadvantageous increase in length of the fiber Bragg grating, these known compensation packages generally requires identification of a material (or combination of materials) which provides an exactly compensating effective thermal coefficient of expansion throughout the entire wavelength range.
Although known temperature compensation packages have decreased the sensitivity of the packaged fiber Bragg grating, these known structures suffer from certain disadvantages. For example, these known structures are often difficult to mass produce, and also tend to retain a significant amount of temperature sensitivity. While the remaining temperature sensitivity variation of known compensated fiber Bragg gratings is acceptable for some uses, it may be unacceptable for use in some dense wave division multiplex systems.